Reflex xerography



Dec. .15, 1959 J. F. BYRNE 2,917,385

REFLEX XEROGRAFHY Filed Aug. 26, 1955 GENERATlNG ELECTRKLLY lMAGEMARKlNG 'SAPCI-ILINC DEVELOPMENT NwR PARTCLES PARTICLES FlXAT|QN IMAGEFoRMAnoN Fg 1 f PLATE SENSITIZATION JOHN F. BYRNE ATTOR JE'Y UnitedStates Patent() REFLEX XEROGRAPHY John F. Byrne, Columbus, Ohio,assignor, by mesne aslgninents, to Haloid Xerox Inc., a corporation ofNew .Application August 26, 1955, Serial No. 530,700

14 Claims. (Cl. 96-1) This invention relates to xerography andparticularly to a Xerographic plate and a method of using it.

In Xerography it is usual to form an electrostatic latent image on asurface. One method of doing this is to charge a photoconductive,insulating surface and then dissipate the charge selectively by exposureto a pattern of activating radiation. Other means of formingelectrostatic latent images are set forth in U.S. 2,647,464 to James P.Ebert. Whether formed by these means or any other, the resultingelectrostatic charge pattern is conventionally utilized by thedeposition of an electroscopic material thereon through electrostaticattraction whereby there is formed a visible image of electroscopicparticles corresponding to the electrostatic latent image.Alternatively, the electrostatic charge pattern may be transferred to aninsulating lrn and the electroscopic particles deposited thereon to formthe visible image. In any case, this visible image, in turn, may betransferred to a second surface to form a Xerographic print.

Previously it has not been possible to utilize the xerographic processwith reflex-type exposure. The mechanism of conduction in aphotoconductive material in general involves the liberation of holes orelectrons (depending on the material) due to absorption of light quanta.Thus, in the thicknesses generally used for photoconductivity thephotoconductive layer is relatively opaque. Further, any illumination ofsuflicient intensity to penetrate the photoconductive layer would besufficient itself to discharge any electrostatic charge placed on thephotoconductive layer in a sensitizing process irrespective of anyadditional radiation reflected back to the photoconductive surface fromany image surface as in a reflex system.

However, a reex system has many advantages over other reproductionmethods. The reex principle is used in many processes in the graphicarts eld. Two of the main reasons are the savings possible-savings ofmoney and space. In a reflex system lenses are not necessary. Lenses ofgood optical quality are expensive. Their elimination is an appreciablesaving. Further, placing the copy either in contact with the plate oralmost so rather than at a distance determined by the focal length ofthe lens `system makes possible substantial reductions in spacerequirements with consequent increased flexibility of design.

There has now been discovered a novel image bearing member which nowmakes possible reflex copying in a xerographic system. For a betterunderstanding of this invention, reference is now directed to thefollowing description taken in connection with the accompanyingdrawings. The scope of my invention will be pointed out in the appendedclaims.

Fig. l of the attached drawings is a block diagram showing the positionof the development step in an overall xerographic process which resultsin a visible image;

Fig. 2 is an isometric drawing of a xerographic plate .embodying.featuresof the present invention withv a cut- 2,917,385 Patented Dec.15, 1959 away section to facilitate illustration of the construction ofthe plate;

F Fig. 3 is a fragmentary cross section of the plate of Figs. 4, 5, and6 are similar views of a cross section of Fig. 2 illustrating theformation of an electrostatic image thereon according to one embodimentof the invention; and

Fig. 7 is a fragmentary cross section of apparatus according to anotherembodiment of the invention.

Fig. 8 is a fragmentary cross section of a xerographic plate accordingto another embodiment of the invention.

Fig. 9 is a fragmentary cross section of a xerographic plate accordingto still another embodiment of the invention.

The present invention contemplates a xerographic plate comprising atransparent or translucent conductive support for a pattern of opaqueconductive material, each opaque pattern portion itself being covered bya layer of a photoconductive insulating material and a method ofxerography in which the exposure of the Xerographic plate isaccomplished by passing light through the backing of the plate. Theexposure of the plate is preferably accomplished by reflection of lightfrom the sheet to be copied and the invention contemplates within itsscope a new method of xerography embodying such a mode of exposure.

While a preferred embodiment of the invention is described herein, it iscontemplated that considerable variation may be made in the method ofprocedure and the construction of parts without departing from thespirit of the invention. In the following descriptions and in theclaims, parts will be identified by specic names if convenient but theyare intended to be as generic in their application as similar parts ofthe art will permit. For greater ease in comprehension, where the samepart appears in more than one figure the same number will be appliedthereto in each ligure.

As shown in Fig. l, the general Xerographic process involves theformation of an electrostatic image. This is generally, although notalways, preceded by a treatment to sensitize the surface on which theelectrostatic image is to be formed. The electrostatic image to beuseful must then be rendered visible, which is done in a developmentstep. This is accomplished by depositing electroscopic particles eitheron the surface on which the image was formed or on an insulating surfaceto which the electrostatic image has been transferred. The basicxerographic process is set forth in some detail in U.S. Patent 2,297,691to Chester F. Carlson.

In the preferred method of reliection copying of the present inventionthe transparent or translucent Xerographic plate is electrically chargedto provide a resident charge on the surface of the photoconductiveinsulating pattern and the plate is then placed against the sheet to becopied with the photoconductive insulating pattern facing the sheet.Light is then passed through the plate from behind and the opaqueconducting pattern prevents the light from illuminating, and thereforedischarging, the photoconductive insulating material which overlies onlythe opaque conducting material. The light passes through the transparentor translucent interstices in the opaque pattern to illuminate thesurface of the sheet to be copied. Where the light strikes a black areaof the sheet it is ylargely absorbed. However, in the white areas of thesheet a portion of the light is reflected into the photoconductivematerial overlying the opaque conductive pattern. Since thephotoconductive insulating material is rendered conductive byillumination, the portions of the photoconductive material receivingreflected light from the white areas of the sheet being copied arepartly or fully discharged. There is thus left on the plate a series ofcharged areas only where black areas appear on the sheet being copied.After exposure the plate is developed by depositing a timely-dividedelectrostatically attractable material as described, for example, in theabove-mentioned Carlson patent or in U.S. Patent 2,618,552 to E. N.Wise. Alternatively, the paper, plastic or other material on which it isdesirable to place the visible image may itself be placed in contactwith the xerographic plate bearing the electrostatic image and theelectrostatically attractable material deposited directly thereonthereby obviating the necessity for transferring the developed imagefrom the plate to the paper as well as eliminating having to clean theplate.

Referring to Figs. 2 and 3, the xerographic plate 16 illustrated thereincomprises a transparent sheet backing such as a plate of glass or oftransparent plastic material such as polystyrene, polymethylmethacrylate, cellulose acetate or other similar transparent sheetmaterial. The plate may be sufiiciently thick and rigid to besubstantially non-liexble, or the backing 10 may, if desired, beflexible enough to permit bending, rolling, or winding the plate.Backing 10 may itself be conductive or, as here, be coated with atransparent conductive layer 11, such as tin oxide on a glass backing.On top of the transparent conductive layer 11 is placed a pattern ofopaque conductive material 12 such as aluminum, silver, etc. Forconvenience this pattern will be termed a dot pattern although it isunderstood that no limitation is placed on the geometrical shape of theindividual particles of the pattern. On top of the individual dots 12 ofthe opaque conductive material is placed a coating of a photoconductiveinsulating material 13 such as selenium, sulfur, anthracene, etc. Thedot pattern desirably has between 100 and 500 or more dots per linearinch and the number preferably exceeds 200 per inch. In the drawing thesize of the dots has been exaggerated to more clearly depict theirstructure. While the opaque conductive material 12 is shown as beingbroken up into a dot pattern by both horizontal and vertical separations1S, if desired the opaque material 12 may be divided only by parallellines running either horizontally, vertically, or diagonally. In thiscase the dot pattern would be in the form of parallel lines of opaqueconductive material. In the preferred embodiment the opaque material isdivided both horizontally and vertically, the width of each opaqueparticle being substantially equal to the spacing between particles.

Dot patterns may be applied to the plate in several ways. One methodcomprises placing against the face ofy conductive coating 11 'a maskhaving a dot pattern therein as is used in making color TV tubes or amask comprising merely a frame supporting a series of fine parallelwires. The assembly is then placed in a vacuum and a metal such asaluminum, silver, lead, tin, copper, or the like is evaporated onto thelayer 11 until a sufciently non-transparent layer is built up betweenthe interstices of the mask. The evaporation of the metal is thenstopped and a photoconductive insulating material such as selenium,sulfur, anthracene, or mixtures thereof, evaporated on top of the opaquemetal coating. The photoconductive insulating coating may be anywherefrom a few microns to a few hundred microns thick. When the desiredthickness has been attained air is admitted and the mask removed toleave the dot pattern on the plate. Desirably the plate 10 is positionedon a platen which maintains the assembly at a xed temperature duringdeposition. For deposition of selenium a temperature of about 60 to 80C. is desirable.

Another method of applying a dot pattern comprises spraying onto theplate a suspension of finely divided opaque conductive material asgraphite, metal, or other material, with a resin binder in a solvent forthe binder such as alcohol using the mask previously described. Thephotoconductive insulating material may also be applied Cil in a resinbinder, thus eliminating the necessity for vacu uum apparatus.

A further method comprises placing on layer 11 rst a uniform coating ofopaque conductive material followed by a uniform coating ofphotoconductive material either by vacuum evaporation or by solventapplication of a finely ground dispersion in a resin binder. The platethen has parallel lines engraved into the transparent conductive coating11 using a mechanical engraver. The groove can also be formed in theplate by chemical etching, using a masking material such as a waxcoating to cover the intervening spaces.

Another method of forming the grid comprises again applying uniformlayers of opaque conductive metal and photoconductive material followedby coating the photoconductive material with a thin layer of bichromatedgelatin and exposing to an optical image of the grid after which thenon-exposed intervening material is removed. The areas not protected bythe hardened gelatin are then removed by chemical etching after whichthe hardened gelatin is removed, as by hot water.

If desired the dot pattern instead of extending above the surface of theplate as shown in Figs. 2 and 3 may be countersunk into the surface togive a smooth-faced plate. This may be done by etching or pressinghollows which are tilled with layers 12 and 13. Such a plate is shown inFig. 8. A smooth-faced plate has obvious advantages such as improvedcleanability, etc. The process for using such a plate is of course thesame as that described for the plate of Figs. 2 and 3.

Where the photoconductive material is applied in a resin binder, notonly may materials such as selenium, sulfur, anthracene, etc. in aiinely ground condition be used, but also photoconductive phosphors suchas zinc oxide, zinc sulfide, cadmium sulfide, cadmium selenide, mixturesthereof, lead iodide, lead chromate, etc. Suitable resin binders includevinyl resins,v silicones, cellulose esters and ethers, natural resinssuch as shellac, etc. Inorganic binders such as sodium silicate may alsobe used.

Figs. 4, 5, and 6 illustrate a method of operation using such a plate.As shown in Fig. 4, a uniform electrostatic charge is first placed onthe photoconductive insulating material, thereby sensitizing the plate.Any means of doing this known to those skilled in the art may be used.Examples are frictional charging as disclosed in the above Carlsonpatent, and applying an ion current as from a corona generating means asin U.S. 2,705,675 to W. E. Bixby or from a radioactive source in thepresence of an electrostatic eld as in U.S,. 2,701,764 to Chester F.Carlson. The plate is now sensitized and must be kept in the dark. Thedistribution of electrostatic charges 14 is as shown in Fig. 4. Next asheet of copy to be reproduced 20 having thereon a dark image area 21and a white non-image area 22 is placed against the sensitizedphotoconductive insulating layer as shown in Fig. 5. In general the copyshould be placed close enough to the plate so that spreading of thereflected light does not seriously affect image quality. Light nowilluminates the plate from a suitable source 30, as a light bulb. Thelight passes through the transparent backing 10. Where a light ray hitsthe opaque material 12 it is reected. In the areas between the opaquedots 12, nothing reflects the light and, accordingly, it passes throughthe open areas 15 in the dot pattern and illuminates the copy 20. Wherethe light strikes the dark image areas 21, it is absorbed thereby. Thus,the photoconductive dots immediately underneath the dark image areas arenot discharged and retain their electric charge. Where the light strikesthe white non-image areas 22 of the copy 20 a portion of the light isreflected and scattered, thereby striking the photoconductive material13. Wherever the photoconductive material is struck by light it isrendered Conductive, thereby permitting the charge on the surfacethereof to pass through into the opaque conductive portion of the dotpattern 12 and in turn to the .transparent S conductive layer 11. Afterexposure, there will be a distribution of charge on the plate as shownin Fig. 6, wherein the image areas 21 represent charged areas on theplate and non-image areas 22 are represented by yplate areas having noelectrostatic charge thereon.

This electrostatic image is then rendered visible by `depositingelectrostatically attractable material thereon as shown either in U.S.2,297,691 or U.S. 2,618,552, or any other means known to those skilledin the art. Alternatively, the paper or plastic on which it is desiredto place a visible image may be placed directly on the plate surfacebearing the electrostatic latent image. The electrostaticallyattractable material is now deposited directly on the surface of thepaper or plastic underlying the Xerographic plate. This eliminates thenecessity of cleaning the plate when development takes place directly onthe plate and makes possible the preparation of multiple copies from oneelectrostatic image. The electrostatic image may also be transferred toa sheet of insulating 'material such as polyethylene terephthalate anddeveloped thereon.

For better image quality, it is desirable to position a -conductiveelectrode, as either a continuous conductive surface or a grid ofconductive material as wires, relatively closely to the surface of thepaper or plastic. This conductive grid, termed a development electrode,is desirably grounded and will act to pull the lines of force externallyabove the electrostatic image-bearing surface, thereby facilitating thedeposition of developer particles. Spacing desirably should be no morethan 1/z inch from the image bearing surface and preferably no more thanabout 1/40 inch or less, whatever minimum spacing is permitted by thesystem selected for deposition of electroscopic powder.

Where the developer has a resin base as in U.S. 2,618,552, it may befixed to the paper or other record material by fusing as by suicienttemperature to melt `the resin and cause it to adhere to the paper, orby application of solvent vapors to tackify the resin. Where thedeveloper particles consist of dye particles, they may be iixed to thepaper by dampening the paper. Spraying the paper with a selectivecoating as an acrylic resin, shellac, or the like, also may be used.Other means of fixing the visible image will at once be obvious to thoseskilled in the art.

Fig. 7 shows an alternative embodiment of the present invention. A platehaving a dot pattern as shown in Figs. 2 and 3 has a sheet of copyplaced in contact therewith as shown in Fig. 5. Unlike Fig. 5, there isno prior sensitization of the Xerographic plate to apply a uniform.electrostatic charge to the photoconductive material. In back of thecopy 20 is placed a conductive electrode 40. A source of potential isthen applied between electrode 40 and the transparent conductive layer11. With this voltage applied, the copy is then illuminated by passinglight through the transparent plate 10. The light which passes throughthe interstices 15 in the opaque pattern is reected back to thephotoconductive dots of the white non-image areas causing charge to flowin those areas only. Where the light strikes the dark image areas 21, nolight is reflected, the photoconductive dots immediately thereunder arenot rendered conductive, and no current ows. In the non-image areas,however, with the polarity of charge as shown applied between 11 and 40,positive charge will flow to the top of the photoconductive material 13.When the illumination is turned off, a positive charge will then betrapped in the non-image areas of the Xerographic plate. This gives anegative electrostatic image of the original copy. Where oppositelycharged developer particles are used to develop the image, a negativevisible image will be developed. Where developer particles having thesame polarity as the image are used, a positive visible image will beobtained. If desired the copy may be omitted and uniform illuminationapplied. This will result in uniform sensitization of the plate. Thecopy is then positioned, exposed, and the plate developed as in Figs. 5and 6.

Where the sheet to be copied 20 has undesirable electrical properties soas to cause lateral conductivity on the face of the xerographic plate,it may be necessary to place a thin transparent insulating material 50,as a tilm of polyethylene terephthalate, between the copy and the plate.

This method of forming an image shown in Fig. 7 also makes possible theutilization of the type of smooth-faced plate shown in Fig. 9. The plateis similar to that shown in Figs. 2 and 3 except that the interstices 15between the dots are iilled with any transparent or translucentinsulating material 17 such as polystyrene, sodium silicate, vinylresins, cellulose esters and ethers, urea-formaldehyde resins,silicones, etc. The material 17 must be transparent or translucentenough to permit the light to reach the copy. In case the material 17 isapplied in such a manner as to cover all or part of the dots, the platemay be subjected to a careful grinding or polishing if it is desired tohave a surface consisting of alternate areas of material 17 andphotoconductor 13. If desired, however, a layer of transparentinsulating material either the same as or different from that used for17 may be applied to cover the photoconductor 13 with a protectivecoating a few microns (say 3-15) thick. Such a layer would protect thephotoconductor from abrasion and thereby extend the life of the plate.The use of the process of image formation illustrated in Fig. 7 with theplate of Fig. 9 eliminates the problem of the charge placed on material17 by prior sensitization with a corona.

While the present invention has been described herein as carried out inspecific embodiments thereof, there is no desire to be limited thereby,but it is intended to cover the invention broadly within the spirit andscope of the appended claims. Thus the novel xerographic platesdescribed herein while particularly adapted to a reflex copying systemare not necessarily limited thereto but may be utilized in a regularxerographic copying process.

I claim:

1. A xerographic plate comprising as an integral member a continuoussolid support having la uniform pattern of finely-interspersedtransparent and opaque areas, at least the opaque areas beingelectrically conductive, a photoconductive insulating material coated onand covering only said opaque areas so that illumination through saidsupport passes through said plate in one direction without activatingsaid photoconductive insulating material, and means to apply a groundpotential to each of the conductive opaque areas in said support layer,said plate being adapted to be electrostatically charged on the surfaceof said photoconductive insulating material, and uniformly illuminatedthrough said support while a facsimile copy contacts saidphotoconductive insulating material.

2. A xerographic plate as claimed in claim 1 in which said means toapply a ground potential comprises having as said support a transparentelectrically conductive material.

3. A xerographic plate as claimed in claim 1 in which said support is atransparent insulating material in which said means to apply a groundpotential comprises a uniform layer of transparent electricallyconductive material coated on said support.

4. A xerographic plate as claimed in claim 1 in which said opaqueelectrically conductive areas having thereon a photoconductiveinsulating material are recessed into the surface of said plate so thatthe said plate is smooth faced.

5. A Xerographic plate as claimed in claim 1 in which the areas betweensaid opaque electrically conductive areas having thereon aphotoconductive insulating material are filled with a transparentmaterial so that the said plate is smooth faced.

6. A xerographic plate as claimed in claim 1 in which thephotoconductive insulating material is vitreous selenium.

7. A Xerographic plate comprising as an integral member a continuoussupport having a uniform pattern of nely interspersed transparent anddiscontinuous, discrete opaque areas, at least the opaque areas beingelectrically conductive, a photoconductive insulating material coated onand covering only said opaque areas so that illumination through saidsupport passes through said plate in one direction without activatingsaid photoconductive insulating material, and means to apply a groundpotential to each of the conductive opaque areas in said support layer,said plate being adapted to be electrostatically charged on the surfaceof said photoconductive insulating material, and uniformly illuminatedthrough said support while a facsimile copy contacts saidphotoconductive nisulating material.

8. A Xerographic plate as claimed in claim 7 in which said opaqueconductive areas are composed of metal.

9. A Xerographic plate as claimed in claim 7 in which said opaqueelectrically conductive areas are composed of a timely-ground opaqueelectrically conductive material dispersed in a binder.

10. A Xerographic plate as claimed in claim 7 in which thephotoconductive insulating material is vitreous selenill. A method ofXerography which comprises electrostatically charging the surface of alayer of photoconductive insulating material arranged in a dot patternon a light transmitting electrically conductive support, contacting saidsurface with a facsimile original to be copied, uniformly illuminatingsaid layer so as to project light through said layer onto said facsimileoriginal whereby the diierential reflection of light from said originalcreates an electrostatic charge pattern on said photoconductiveinsulating material corresponding to said copy, cutting off said light,removing said layer from said original, positioning an electricallyinsulating sheet on said surface, and depositing a nely-divided,electrostatically attract, able material on said sheet in conformitywith said electrostatic image.

12. A process according to claim 11 including the added step of drawingthe lines of force of said electrostatic image externally through saidsheet while depositing said electrostatically-attractable material.

13. A method of xerography which comprises placing an electricallyinsulating transparent pellicle on the surface of a layer ofphotoconductive insulating material arranged in a dot pattern on alight-transmitting electrically conducting support, placing a facsimileoriginal to be copied on said pellicle facing said surface, positioningan electrically conductive electrode on the side of the original not incontact with said pellicle, connecting a source of potential betweensaid conductive support and said conductive electrode, uniformlyilluminating said layer so as to project light through said support andsaid pellicle onto said original while said potential source isconnected, the differential reilection of light from said originalcreating an electrostatic charge pattern on said photoconductiveinsulating material corresponding to said original, then cutting offsaid light, removing said original from contact with said pellicle anddepositing finely-divided electrostatically attractable material on saidpellicle in conformity with said electrostatic image.

14. A process according to claim 13 including the added step of drawingthe lines of force of said electrostatic image externally through saidsheet while depositing said electrostatically-attractable material.

References Cited in the file of this patent UNITED STATES PATENTS2,026,292 Van der Grinten Dec. 31, 1935 2,051,583 Van der Grinten Aug.18, 1936 2,297,691 `Carlson Oct. 6, 1942 2,572,497 Law Oct. 23, 19512,599,542 Carlson June 10, 1952 2,672,416 Stanton Mar. 16, 19542,673,153 Talbot Mar. 23, 1954 2,725,304 Landrigan Nov. 29, 19552,727,808 Thomsen Dec. 20, 1955 2,764,693 Jacobs et al Sept. 25, 19562,803,542 Ullrich Aug. 20, 1957 2,808,328 Jacob Oct. 1, 1957 2,833,648Walkup May 6, 1958 OTHER REFERENCES Van der Grinten: The PhotographicJournal, vol. LXXVII, September 1938, pages 579-583. (Copy in Sci.Libr.)

Wainer: Phot. Eng., 1952, vol. 3, No. 1, pages 12 to 22. (Copy inScience Library.)

1. A XEROGRAPHIC PLATE COMPRISING AS AN INTEGRAL MEMBER A CONTINUOUSSOLID SUPPORT HAVING A UNIFORM PATTERN OF FINELY-INTERSPERSEDTRANSPARENT AND OPAQUE AREAS, AT LEAST THE OPAQUE AREAS BEINGELECTRICALLY CONDUCTIVE, A PHOTOCONDUCTIVE INSULATING MATERIAL COATED ONAND COVERING ONLY SAID OPAQUE AREAS SO THAT ILLUMNATION THROUGH SAIDSUPPORT PASSES THROUGH SAID PLATE IN ONE DIRECTION WITHOUT ACTIVITINGSAID PHOTOCONDUCTIVE INSULATING MATERIAL, AND MEANS TO APPLY A GROUNDPOTENTIAL TO EACH OF THE CONDUCTIVE OPAQUE AREAS IN SAID SUPPORT LAYER,SAID PLATE BEING ADAPTED TO BE ELECTROSTATICALLY CHARGED ON THE SURFACEOF SAID PHOTOCONDUCTIVE INSULATING MATERIAL, AND UNIFORMLY ILLUMINATEDTHROUGH SAID SUPPORT WHILE A FACSIMILE COPY CONTACTS SAIDPHOTOCONDUCTIVE INSULATING MATERIAL.